1. Field of the Invention
The present invention relates to an information selection device of a disc player and particularly to an information selection device which can rapidly search a desired piece number and a desired index on a disc where a plurality of pieces are optically recorded so that the disc player can start to play the music of the desired piece number and index.
2. Description of the Prior Art
A disc player which uses an optical pickup to reproduce a digital signal from a disc where concavities and convexities corresponding to the digital signal are engraved, for example, a digital audio disc player is well-known in the art. In the case of a digital audio disc player currently put on the market, an index of a disc called a table of contents (TOC) is recorded on a lead-in track located on the innermost circumference of the disc and this TOC includes data on the pieces recorded on the disc indicating a time code value of each piece, that is, the time represented as minutes and seconds when each piece is to be played from the first track of the program area of the disc. Subcodes in each frame of the signal contain data on the piece number and the index which the signal frame belongs to, the time represented as minutes and seconds required from the first track of the program area, etc. If the disc thus structured is set in a play mode, the disc player first reads and stores the above described TOC.
Such a conventional digital audio disc player uses a method for rapidly searching a track to be started, that is, a target track of a desired piece out of a plurality of pieces recorded on a disc. Such a method is disclosed for example in the Japanese Patent Laying-Open Gazette No. 8695/1980 (U.S. Pat. No. 4,506,355). According to the method disclosed in this gazette, the first means first selects a target address of a target track of a desired piece to be played. Then, in a search mode period, that is, in a period when the moving means moves the incident beam relatively toward the disc so that the incident beam crosses the tracks, the second means monitors the modulated beam so that the address of the track hit by the incident beam is detected from the information recovered by the hitting of the incident beam onto the disc. In this search mode period, the third means detects an indication of the distance between the target track and the hitting point of the incident beam and the moving means is adjusted by the control means so that the distance between the hitting point of the incident beam and the target track may be decreased. As the above described distances is decreased, the moving speed of the beam is reduced. When the target track is detected, the control means stops the moving means to bring the search to an end.
More specifically described, the indication of the distance between the target track and the hitting point of the incident beam can be obtained by detection of a difference between the time period converted based on the distance from the lead-in track to the track hit by the incident beam and the time period converted based on the distance from the lead-in track to the target track. In other words, when the piece number of a desired piece to be played is designated, the time period required from the first track of the program area of the disc to the track at the start of the designated piece is determined from the content of the TOC stored in the disc player as described above and this time period is regarded as the target time. In addition, the time period required from the first track of the program area to the track hit by the radiated beam at present is determined by the subcode in each frame of the signal. Accordingly, the distance between the target track and the hitting point of the incident beam can be determined as the time by detection of a difference between the above described target time and the time required to attain the track hit by the beam. According to the magnitude of the indication of the distance, the moving speed of the moving means is determined by steps and as a result, the hitting point of the incident beam never exceeds the target track and the target track can be searched rapidly.
As described above, the TOC stores the time from the first track of the program area to the track at the start of each piece, that is, the "absolute time (A time)". However, the TOC does not store the A time from the first track of the program area to each index existing within each piece and consequently, the indexes existing within each piece cannot be searched directly.